which item is used to supply some of the fuel needed by the brain only after the body has been fasting for a while

Sugar

Explanation:

    To handle all of its tasks, the brain consumes one-fifth of all the energy our bodies produce. And its main fuel is glucose (which we popularly call sugar). Every minute, this organ alone uses 5.6 milligrams of this nutrient for every 100 g of its weight.

the answer is; comparing the frequency of collisions with and without the device

this makes the anti-collision system an independent variable and the collisions a dependent variable. if there are fewer collisions with an anti-collision system that without, then it can be stated that the system is a success. essentially, collisions under an anti-collision system are compared with the frequency of collisions by cars with the human drivers.